Parylene deposition chamber and method of use

ABSTRACT

Disclosed is an improved parylene deposition chamber wherein reactive monomer vapors enter the chamber tangentially so as to create a rotational flow of vapor within the interior of the chamber. A substrate support fixture is psoitioned within the chamber and rotated in a direction counter to the rotational flow of vapor. An annular space exists between the outer edge of the fixture and the inner wall of the chamber so as to allow the rotating vapor to descend freely within the chamber. Waste of parylene chemicals is minimized by eliminating the need for the positioning of baffles within the chamber.

This application is a division of application Ser. No. 07/211,338, filed6/23/88, now U.S. Pat. No. 4,945,856.

BACKGROUND OF THE INVENTION

This invention relates generally to an improved device for use indepositing condensation coatings on various substrates. Moreparticularly, the invention relates to an improved modular depositionchamber for depositing para-xylylene polymers on electrical componentparts and the like.

Para-xylylene polymers are employed as coatings for various electroniccomponents due to their desirable physical and electrical properties.One advantage of poly-para-xylylene coatings is that extremely thinlayers of such coatings are capable of exhibiting highly desirablephysical and electrical properties. Because para-xylylene coatings areapplied in very thin layers, heat tends to dissapate rapidly from theunderlying components. Thus, the coated components cool down quickly andare less prone to temperature related degredation than similarcomponents bearing other types of coatings.

In further contrast to conventional polymer coatings, para-xylylenes aregenerally not prepolymerized prior to application on the coatablesubstrate. This is so because the para-xylylene polymers are not givento simple extrusion, melting or molding as are many of the conventionalthermoplastics. Additionally, because the para-xylylenes are generallyinsoluble in commonly used organic solvents, it is impractical to employtraditional solvent deposition techniques for applyingpoly-para-xylylene coatings.

Accordingly, in most commercial applications, para-xylylene polymers aredeposited on desired substrates by a pyrolytic deposition process knownspecifically as the "parylene process." Such process begins with thevaporization of a cyclic di-para-xylylene dimer. The dimer ispyrolytically cleaved at temperatures of about 400° to 750° C. to form areactive para-xylylene monomer vapor. Thereafter, the reactive monomervapor is transferred to a deposition chamber wherein the desiredsubstrates are located. Within the deposition chamber, the reactivemonomer vapor condenses upon the desired substrates to form apara-xylylene polymer or co-polymer film.

Any monomer vapor which fails to condense within the deposition chamberis subsequently removed by a cold trap which is maintained atapproximately -70° C.

The entire parylene process is generally carried out in a closed systemunder constant negative pressure. Such closed system may incorporateseparate chambers for the (a) vaporization, (b) pyrolysis, and (c)deposition steps of the process, with such chambers being connected byway of appropriate plumbing or tubular connections.

A primary consideration in the parylene deposition process is theachievement of uniform coating thickness on the desired substrates.Unlike conventional polymer coating systems, the condensation depositionof parylene coatings is capable of depositing even ultrathin filmswithout running or uneven areas resulting upon the substrates, providedthat the monomer vapor is homogeneously and evenly distributed on thesurface of the substrate. Thus, the design and functioning of thedeposition chamber is critical to the achievement of uniform vapordistribution with resultant even coating deposition.

Another important consideration in the parylene deposition process isthe minimization of waste. Currently, parylene raw materials may cost asmuch as $400 to $600 per pound. Thus, there exists substantial economicmotivation to preserve and conserve the parylene materials during thecoating process. One particular area in which a great deal of materialis wasted is on the various internal structures of the prior artparylene deposition chambers. It must be appreciated that thecondensation deposition of coatings is not substrate selective--i.e. thevapors have no way of seeking out only the desired substrate. Instead,the monomer vapor will condense and polymerize on any reducedtemperature object with which it comes in contact. As a result, theentire inner surface, of the chamber, and all of the objects positionedtherein will become covered with the parylene coating. Thus, theinterior of the chamber and any existing hardware must be cleanedperiodically to remove wasted parylene polymer.

The parylene deposition chambers employed in the prior art havegenerally provided less than optimal coating uniformity due to inferiordistribution and homogeneity of the vapor within the deposition chamber.Also, because of the particular chamber design, the prior art depositionchambers are associated with a great deal of waste of the parylenechemicals.

At least one deposition chamber of the prior art employs a system ofbaffles, positioned adjacent a monomer vapor inlet line, so as todisperse the flow of vapor as it enters the deposition chamber. Suchbaffles are intended to uniformly distribute the monomer vaporthroughout the interior of the deposition chamber thereby insuringuniform coating thickness on the desired substrates. In practicalapplication, however, the various baffle designs employed in the priorart devices have failed to provide truly optimal vapor distributionwithin the chamber. As a result, less than optimal coating uniformityhas been realized. Additionally, the presence of such baffles occupiesotherwise useable space within the chamber and results in greatersurface area within the chamber. Such increased surface area,accordingly, increases the amount of parylene waste due to thenonselective deposition of the polymer on the baffles as well as on thedesired substrates.

Also, the deposition chambers of the prior art incorporate substrateholding racks which are supported only by one or more members extendingfrom the bottoms thereof. The absence of any support member fixing thetop end of such holding rack to the surrounding deposition chamberstructures results in a rather unstable arrangement. Specifically, whenrelatively heavy parts are unevenly distributed on the upper shelves ofthe holding rack such rack may tend to lean against the surroundingbaffles or deposition chamber walls.

SUMMARY OF THE INVENTION

The present invention overcomes the above described problems of theprior art, and others, by providing a condensation coating depositionchamber wherein uniformity of monomer vapor is maintained by inducting arotary flow pattern within the chamber. Such rotary flow patternobviates the need for baffles or other hardware elements therebylessening the amount of polymer wasted during the process. Additionally,the parylene deposition chamber of the present invention providesgreater versatility than the prior art devices because it is of modulardesign and, thus, easily detachable from the pyrolytic generating unit.Also, the deposition chamber of the present invention incorporates asubstrate support or holding rack which is pivotally supported at itstop end as well as its bottom end.

In accordance with the present invention, there is provided acondensation coating deposition chamber comprising a tank-like chamberbody having a floor, a cylindrical wall, and an openable and closablelid. The monomer vapor enters tangentially near the top of the chamberthrough a tangentially connected monomer supply line. Such tangentialentry of the monomer vapors results in a generally annular rotationalflow of the vapors as they descend axially through the inner confines ofthe deposition chamber. Further in accordance with the invention asubstrate support fixture is positioned centrally within the depositionchamber. As the flow of monomer vapors descends within the innerconfines of the deposition chamber, the support fixture is rotated,preferably in a direction opposite the rotational flow of the enteringvapors. Also, the fixture is specifically sized such that an annularspace exists between the outer edges of the rack and the inner wall ofthe chamber. The provision of such annular space provides for an evenflow of vapor around the fixture.

Further, in accordance with the invention, the substrate support fixturemay comprise a multi-tiered rack having a plurality of substrate supportshelves positioned horizontally therewithin. Each such substrate supportshelve is provided with a multiplicity of perforations through which themonomer vapor may flow. Such perforations further enhance the degree ofpermeation and evenness of the vapor flow within the deposition chamber.The substrate support fixture is preferably pivotally connectable to thelid of the deposition chamber as well as the floor of the chamber,thereby providing uniform top to bottom support for the substratesupport fixture so as to prevent lateral movement or shifting thereofand avoiding any resultant contact between the edges of the supportfixture with the surrounding deposition chamber wall.

In accordance with an even further aspect of the invention, thedeposition chamber of the present invention may be of modular design soas to be easily detachable from the attendant pyrolytic generationequipment. Such modular design permits the deposition chamber to bemoved to a separate area for loading/unloading, cleaning andmaintenance. Also, upon detachment of one modular chamber, anothermodular chamber may be immediately substituted in its place. Suchflexibility provides for optimal utilization of a single pyrolytic vaporgenerating unit with multiple interchangable deposition chambers.Additionally, to facilitate movement of the modular sections, both thepyrolytic generator and deposition chamber modules are caster mounted topermit rapid and easy relocation as desired.

A principal object of the invention is to provide a condensation coatingdeposition chamber wherein improved vapor flow characteristics anddesign will result in uniform and even coating deposition, even atultrathin film thicknesses.

Yet another object of the invention is to provide a condensation coatingdeposition chamber which will prevent waste of chemicals by avoiding theneed for certain space occupying objects, such as baffles, whichincrease the surface area within the chamber.

Yet another object of the invention is to provide a condensation coatingdeposition chamber which is of modular design so as to be easilyinterchangeable and detachable from the attendant vapor generating unit.

A still further object of the invention, is to provide a substratesupport fixture which is capable of being rotated within the depositionchamber so as to subject each substrate to uniform vapor concentrationsand conditions.

Additional objects and advantages of the invention will become apparentto those skilled in the art upon reading and understanding of thefollowing detailed description and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a parylene coating system whichincorporates the modular parylene deposition chamber of the presentinvention.

FIG. 2 is a schematic diagram of the individual components of a parylenecoating system which incorporates the parylene deposition chamber of thepresent invention.

FIG. 3 is an exploded view of a preferred parylene deposition chamber ofthe present invention.

FIG. 4 is a top plan view showing the rotational flow of vapor within apreferred parylene deposition chamber of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to the drawings wherein the showings are for purposes ofillustrating a preferred embodiment of the invention and not forpurposes of limiting its scope, FIG. 1 is a front view of the modularparylene deposition system of the present invention. Such systemconsists generally of a pyrolytic vapor generating module 10 and anattendant deposition chamber module 12. The exterior of the pyrolyticvapor generating module 10 includes a housing 14 and a control panel 16,as shown.

The base of the vapor generating module housing 14 incorporates astorage area or cabinet for storing spare parts, additional substratefixtures, etc.

The pyrolytic generation module 10 houses conventional means, i.e. (a) acontroller unit (not shown) which controls the temperatures, conditions,opening and closing of valves, etc., (b) a dimer vaporization chamber(not shown) and the pyrolysis chamber (not shown).

The deposition chamber module 12 comprises a base cabinet 18 and adeposition chamber 20. The base cabinet, 18 is sized and configured tohouse an attendant vacuum pump (not shown) and cold trap (not shown), inaddition to acting as a support base for the deposition chamber 20. Thedeposition chamber 20 comprises a generally cylindrical tank having anouter wall 22, and inner wall 24, and a peripheral lip 26 about theupper rim thereof. A hinged lid 28 is attached to the chamber so as tobe pivotally moveable between an "open" and a "closed" position. It willbe appreciated that when the lid 28 is closed, it will form a vaportight seal with the lip 26 so as to prevent the escape of vapors fromthe deposition chamber. In this preferred embodiment, the vapor tightseal is accomplished through the positioning of an appropriately sized"o" ring about the chamber lip 26 and/or corresponding rim of thechamber lid 28.

A vapor inlet line 46 enters the chamber 20 tangentially through aninlet port 30 formed near the top of the chamber. The vapor outlet line32 exits through an outlet port 34 located in the floor 36 of thechamber 20 which is preferably disposed at approximately a 180 degreeoffset from the inlet port 30. Such vapor outlet line is subsequentlyconnected to a cold trap (not shown) and a vacuum pump (also not shown)whereby negative pressure is maintained on the entire system.

The overall pyrolitic coating method of the present invention may beappreciated by referring specifically to the schematic diagram of FIG.2. Vaporization chamber 40 is connected to a pyrolysis chamber 44 by wayof a pipe 42. Thus, the vaporization chamber 40 provides a zone whereina quantity of di-para-xylylene dimer is initially vaporized at elevatedtemperatures. Thereafter, the vaporized dimer is transferred via pipe 42into the pyrolysis chamber 44 wherein the dimer is pyrolized attemperatures of about 400 to 750 degrees C. to form the desiredpara-xylylene monomer. Following pyrolysis, the reactive monomer vaporis transferred via line 46 into the novel parylene deposition chamberentering tangentially near the top of the chamber. Such tangential entrycreates a rotary vapor flow pattern within the chamber.

A substrate holding fixture is positioned within the center of thechamber and, in this preferred embodiment, is rotated in a directionopposite to the rotational direction of the vapor flow by fixture drivemeans 47.

Following deposition and condensation of the coating on the substratescontained within the deposition chamber 20, any residual vapor will exitthe bottom of the deposition chamber 20 via exit line 32. The cold trap48 serves to rapidly condense and polymerize such residual vapors.Vacuum pump 50 is connected to the entire system via vacuum line 52 andmaintains continual negative pressure on the system.

The ability of the present invention to uniformly and evenly depositeven ultra thin parylene coatings is owed in part to the specificconfiguration and mode of operation of a novel substrate holding fixturewhich is positionable within the deposition chamber 20. The specificfunctional features of such substrate holding feature are shown in FIG.3. Specifically, the substrate holding fixture 50 comprises two circularplate-like end panels 52 and 54 with a plurality of vertical supportmembers 56, 58, 60 and 62 extending therebetween. One or more perforatedsubstrates holding shelves 64 are horizontally connected within thevertical support members 56, 58, 60, and 62 so as to provide convenientshelves for stacking the desired substrates to be coated. In thispreferred embodiment, the desired substrates may include such items ascircuit boards, thermistors, sensors, probes, transducers, and similardevices.

The overall diameter of the end plates 52 and 54 will be less than theinside diameter of the chamber 20. Also, the substrate shelves 64positioned between the end plates 52 and 54 will be diametrically equalto or smaller than such end plates. Thus, when the fixture 50 isdisposed centrally within the cylinder 20, there will remain an openannular space 70 between the inner cylinder wall 24 and the outercircumference of the fixture 50. Such annular space 70 is particularlyimportant in permitting the desired rotational or spiral flow of thedescending vapors within the chamber 20 as will be more particularlydescribed herein.

The fixture 50 is connected at its base to a rotatable fixture 66 whichis located at the center of the tank floor 68. By such arrangement, thesubstrate holding fixture 50 may be slowly rotated, preferably in adirection counter to the rotational flow of the entering vapor.

The desired positioning of the fixture is maintained not only by thebottom pivotal connection to the rotatable mounting fixture 66, but alsoby a top pivotal member 7 which extends from the center of the upperplate member 52 and inserts within a locator notch 29 at the center ofthe hinged lid 28. By such arrangement, the substrate holding fixture 50is firmly held in its central position within the chamber such that theannular space 70 around the fixture 50 is maintained.

As is specifically shown in FIG. 4 by the dotted arrows, the reactivemonomer vapor enters tangentially at the top of the cylinder throughvapor entry line 46. The vapor thereafter flows rotationally in a firstdirection (i.e. clockwise) around the annular space 70 and is pulledaxially downward by vacuum existing at outlet port 34 so as toinfiltrate all open areas within the substrate holding fixture 50.

In the showing of FIG. 4, the fixture 50 is being slowly rotated in acounter-clockwise direction as indicated by arrow X. Suchcounter-clockwise rotation of the fixture is opposite to the rotationalflow of the incoming vapor. Such gives rise to uniform dispersion of thevapor as it condenses and polymerizes on the substrate surfaces.

Although the invention has been described herein with respect to apreferred embodiment, numerous modifications and alterations may be madeto the described embodiment without departing from the spirit andintended scope of the invention. For instance, the shape, orientationand/or positioning of the deposition chamber may be altered in many wayswithout preventing or interfering with the intended rotational flow ofvapors within the chamber. Also, the substrate holding fixture may beconfigured in many different ways while still retaining its desiredfunctional capacity.

Accordingly, it is intended to include any and all such modificationsand alterations within the scope of the following claims and/or theequivalents thereof.

What is claimed is:
 1. A parylene deposition system comprising:apyrolytic vapor generating module comprising:a vaporization chamber forvaporizing a quantity of di-para-xylylene dimer; and a pyrolysis chamberconnected to said vaporization chamber, wherein said vaporized dimer maybe pyrolized to form a reactive monomer vapor; and a deposition chambermodule comprising:a closed tank having a lid movable between a firstopen position and a second closed position, said deposition chambermodule including a vapor inlet port and outlet port formed upon saidtank and positioned to provide a flow path for the reactive monomervapor through said tank, said inlet port being disposed upon said tanksuch that the reactive monomer vapor will enter the tank tangentially,and will thereafter flow in a generally rotational path about theinterior of the tank toward said outlet port; a substrate supportfixture positioned within said tank; and means for selectively attachingand detaching said deposition chamber module to said pyrolytic vaporgenerating module.
 2. The modular parylene deposition system of claim 1wherein the deposition chamber module includes a cold trap and a vacuumpump, said vacuum pump being operative to maintain continual negativepressure within the tank and pull said vapor downward through said tanktoward said outlet port thereby infiltrating all areas within thesubstrate support fixture.